The present invention relates to an explosion protected socket of the ignition protected type Ex e "increased safety" for double pin base fluorescent bulbs, including a clamping device which will not permit the bulb pins or wires to come loose and is secured to hold the bulb pins and electrical connecting means associated therewith. The invention further relates to an explosion protected lamp of the ignition protected type Ex e "increased safety" equipped with a fluorescent bulb cover which can be opened, with the lamp having at least two sockets.
Any electrical apparatus that is to be used in an hazardous area must comply with the provisions of Standards which regulate the design and test requirements for said electrical apparatus to prevent ignition of the surrounding potentially explosive atmosphere by said apparatus. Typically, these Standards determine a number of different types of protection, and the present disclosure of the invention refers to the European Standards EN 50 014 to 50 020, 50 028 and 50 029, where these individual types of protection a described in detail. These Standards are harmonized within the sphere of CENELEC and in the Federal Republic of Germany have the designation DIN EN 50 014/VDE 0170/0171, Part 1, to DIN EN 50 020/VDE 0170/0171, Part 7, 9 and 10. Besides these Standards, the previous West German VDE Specifications 0170/0171/2.61 with Amendments continue to apply provisionally.
Specifically the Safety Regulations governing electrical apparatus for potentially explosive atmospheres of the type Ex "e" "increased safety" are the subject matter of DIN EN 50 019/VDE 0170/0171, Part 6. "Increased safety" "e" is defined as being a type of protection by which measures are applied so as to prevent with a major decree of security the possibility of excessive temperatures and of the occurance of arcs and sparks in the interior and on the external parts of electrical apparatus which does not produce them in normal service.
European Standard DIN EN 50 017/VDE 0170/0171, Part 4, contains the specific requirements for the construction and testing of "powder-filled" electrical apparatus, type of protection Ex "q". Powder-filling Ex "q" is a type of protection in which the enclosure of electrical apparatus is filled with a material in a finely granulated state so that, in the intended conditions of service, any arc occurring within the enclosure of said electrical apparatus, will not ignite the surrounding atmosphere.
European Standard DIN EN 50 016/VDE 0170/0171, Part 3, defines the specific requirements for the design and testing of "pressurized apparatus", type of protection Ex "p". Ex "p" is a type of protection by which the entry of a surrounding atmosphere into the enclosure of an electrical apparatus is prevented by maintaining inside said enclosure a protective gas at a higher pressure than that of the surrounding atmosphere.
European Standard DIN EN 50 018/VDE 0170/0171, Part 5, defines the specific requirements for the construction and testing of electrical apparatus with "flame-proof enclosure", type of protection Ex "d". Ex "d" is a type of protection in which the parts which can ignite an explosive atmosphere are placed in an enclosure which can withstand the pressure developed during an internal explosion of an explosive mixture and which prevents the transmission of the explosion to the explosive atmosphere surrounding said enclosure etc.
In plants in which there exists the danger of explosion, fluorescent bulbs are generally employed which have single--pin bases and correspondingly designed bulb sockets. Such special fluorescent lamps with single-pin bases are relatively expensive and not always obtainable. Attempts have therefore been made to construct lamps that meet the ignition protected type Ex e "increased safety" requirements and which are equipped to accommodate normal double pin base fluorescent bulbs. Thus, instead of the older fluorescent bulbs having a diameter of 38 mm, modern fluorescent bulbs having a diameter of 26 mm can also be used which, particularly in comparison with single-pin base fluorescent bulbs, have the advantage of greater light yield. For example, FRG-AS No. 2,512,991 discloses an explosion-proof socket for fluorescent bulbs having double-pin bases, this socket including a rotationally securely encapsulated contact area for closing the circuit of the lamp. A pressure tight encapsulated contact area in the sense of VDE 0171, however, requires considerable structural expenditures, especially when, as in the above described socket, the socket housing is made of insulating material and includes a rotatable socket insert equipped with metal contact springs to accommodate the pins of the fluorescent bulb. The individual elements must then be produced within close tolerances so as to meet the requirements of the standards for ensuring the necessary resistance to instantaneous ignition.
This lamp has receiving devices for making contact and holding the socket pins of a double-pin base fluorescent bulb in which these receiving devices are configured as positively retained and secured clamping devices for the socket pins, with a corresponding current supply being provided. Each socket pin has a terminal clamp which secures it against loosening and which, due to its particular configuration, always ensures sufficient contact pressure and meets the requirements for electrical equipment used in areas endangered by explosion. This ensures that, during operation, no ignitable sparks or arcs can occur at the point of connection so that pressure-tight encapsulated contact chambers etc. can be omitted. The reference, however, does not contain any mention of how a socket for double-pin base fluorescent bulbs is to be structurally designed to realize this general idea.